Abstract: This paper mainly focuses on the flexible workflow dynamic behavior model. Activities dynamic behavior can be divided into self-behavior, nested behavior and collaborative behavior. Self-behavior is the procedure of state transition of activity, and we can define it by describing activity state transition diagram based on ECA rules. Collaborative behavior is the procedure of state transition cooperation between activities and through describing state transition cooperation based on ECA rules, thus we can model the fine-grained nested behavior, control behavior and group behavior. The flexible method is suitable for modeling complex business process.